1. Field of the Invention
The invention relates to one-component blends comprising alkoxysilane-terminated polymers which display a high cure rate at room temperature, and to their use.
2. Description of the Related Art
Polymer systems which include reactive alkoxysilyl groups have been known for a long time. In the presence of atmospheric humidity these alkoxysilane-terminated polymers are capable even at room temperature of undergoing condensation with one another, accompanied by elimination of the alkoxy groups. Depending on the level of alkoxysilane groups present and their structure, the polymers formed by this reaction are primarily long-chain polymers (thermoplastics), relatively wide-meshed three-dimensional networks (elastomers) or else highly crosslinked systems (thermosets).
The polymers in question can be either alkoxysilane-terminated polymers with an organic backbone, e.g., polyurethanes, polyesters, polyethers, etc., described in documents including EP-A-269 819, EP-A-931 800, WO 00/37533, U.S. Pat. No. 3,971,751, and DE 19849 817, or polymers whose backbone is composed wholly or at least partly of organosiloxanes, described in documents including WO 96/34030 and U.S. Pat. No. 5,254,657.
In accordance with the countless possibilities for designing such silane-terminated polymer systems it is possible to vary almost arbitrarily not only the properties of the noncrosslinked polymers or of the polymer-containing mixtures (viscosity, melting point, solubilities, etc.) but also the properties of the finished crosslinked compositions (hardness, elasticity, tensile strength, breaking extension, heat resistance, etc.). Just as diverse, accordingly, are the possibilities for use of such silane-terminated polymer systems. Thus they can be used, for example, for producing elastomers, sealants, adhesives, elastic adhesive systems, rigid and flexible foams, any of a wide variety of coating systems, and in the medical sector, for example, for impression compounds in the dental sector. These products can be applied in any form, such as by brushing, spraying, pouring, pressing, troweling, etc.
A disadvantage of all known alkoxysilane-terminated polymer systems, however, is their no more than moderate reactivity toward moisture, either in the form of atmospheric humidity or in the form of (optionally added) water. In order to achieve a sufficient cure rate at room temperature, therefore, it is vital to add a catalyst. The principal problem of doing so is that the organotin compounds generally employed as catalysts are toxicologically objectionable. Moreover, the tin catalysts often still contain traces of highly toxic tributyltin derivatives.
The relatively low reactivity of the alkoxysilane-terminated polymer systems is a particular problem when the terminations used are not methoxysilyl terminations but rather the even less reactive ethoxysilyl terminations. And yet in many cases ethoxysilyl terminated polymers would be particularly advantageous, since the only elimination product of their curing is ethanol.
In order to get around this problem searches have already been undertaken for tin-free catalysts. Consideration may be given here in particular to titanium catalysts, e.g., titanium tetraisopropoxide or bis(acetylacetonato)diisobutyl titanate (described in documents including EP 0 885 933). These titanium catalysts, though, have the disadvantage that they cannot be used together with many nitrogen compounds, since in that case the latter act as catalyst poisons. The use of these nitrogen compounds, as adhesion promoters for example, would be desirable in many cases, however.
Of great advantage would therefore be alkoxysilane-terminated polymer systems which inherently have such high reactivity that the amount of tin catalyst could be greatly reduced. Of particular advantage in this context would be the ability to do entirely without tin and other heavy metal catalysts.